Digital video and audio signal recording apparatus

ABSTRACT

A digital signal recording apparatus is arranged to be capable of permitting long-time recording on one and the same recording medium without impairing the quality of audio signals at all. The apparatus has a first mode in which a digital video signal supplied from a video input circuit and having the amount of information not compressed by a video compression circuit is recorded on the recording medium by a recording circuit while all of n channel digital audio signals supplied from an audio input circuit are recorded by the recording circuit; and a second mode in which the digital video signal having the amount of information compressed by the video compression circuit and only part of the n channel digital audio signals supplied from the audio input circuit are recorded by the recording circuit.

This application is a division of application U.S. Ser. No. 08/541,981,filed Oct. 10, 1995, now U.S. Pat. No. 5,541,739, which is acontinuation of U.S. Ser. No. 08/201,071, filed Feb. 24, 1994,abandoned, which is a continuation of U.S. Ser. No. 07/713,407, filedJun. 11, 1991, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an audio signal recording apparatus and moreparticularly to an apparatus which records an audio signal as a digitalsignal.

2. Description of the Related Art

A digital recording apparatus which records video and audio signals asdigital signals on a magnetic tape with a rotary head in a helicalscanning manner is known by the name of a digital VTR. In the case of ananalog VTR which records video and audio signals as analog signals on amagnetic tape in the helical scanning manner, the VTR is arranged to beoperable either in a standard-time recording/reproducing mode in whichrecording and reproduction can be performed for a standard length oftime (hereinafter referred to as the SP mode) or in a long-timerecording/reproduction mode in which recording and reproduction can beperformed over a longer period of time (hereinafter referred to as theLP mode). The digital VTR of the above-stated kind is also arranged topermit recording and reproduction in the LP mode by compressing therecordable amount of data per unit time.

FIG. 1 is a block diagram showing in outline the arrangement of theconventional digital VTR. An input terminal 10 is arranged to receivethe luminance signal component Y of a video signal. Input terminals 12and 14 are arranged to receive the chrominance signal components PR andPB of the video signal. Input terminals 16, 18, 20 and 22 are arrangedto receive audio signals of four channels. The analog signals suppliedto these input terminals 10 to 22 are digitized by A/D converters 24,26, 28, 30, 32, 34 and 36. The digital video signal data which is thusobtained is temporarily stored by a memory 38V. The digital audio signaldata thus obtained is temporarily stored by a memory 38A. A videoencoder 40 is arranged to perform a recording processing action on thevideo data stored in the memory 38V before recording it on a recordingmedium. An audio encoder 42 is arranged to perform a recordingprocessing action on the audio data stored in the memory 38A also forrecording on the recording medium. An adder 44 is arranged to addtogether (time-base multiplex) the output of the video encoder 40 andthat of the audio encoder 42 and to output them in a time-basemultiplexed state. A recording amplifier 46 is arranged to amplify theoutput of the adder 44. A rotary head 48 is arranged to record theoutput of the recording amplifier 46 on a magnetic tape 50 byelectro-magnetically converting the output of the amplifier 46.

However, if recording is performed in the LP mode capable of recordingfor a period of time which is, for example, twice as long as the time ofthe SP mode, the above-stated arrangement presents a problem which is asdescribed below:

In the case of an analog VTR, the amount of information of the analogaudio signal to be recorded in each track changes little in the LP mode,since it is only the track pitch that is reduced to one half while thenumber of tracks formed per unit time remains unchanged. Further, evenin the event of an analog VTR which is arranged to record a digitalaudio signal along with an analog video signal, the amount ofinformation of the audio signal does not change at all.

Whereas, in the case of the digital VTR, the number of tracks formed perunit time becomes 1/2 of it. Therefore, the amount of information of theaudio signal to be recorded per unit time also must be reducedaccordingly. However, a mere arrangement to perform high-efficiencyencoding by utilizing the correlation of signals in reducing the amountof data of the audio signal of each channel to 1/2 of it greatlydegrades the quality of the audio signal, because: unlike the videosignal, the audio signal does not have much correlation between adjacentsamples. Besides, for the audio signal, it is impossible to use anytwo-dimensional correlation (obtained in the vertical direction of animage) or three-dimensional correlation (in the direction of time).

SUMMARY OF THE INVENTION

Such being the background situation, it is an object of this inventionto provide a digital video and audio signal recording apparatus which iscapable of retaining an adequate tone quality even in the event of asmall amount of audio information per unit time.

It is another object of the invention to provide a digital videorecorder which is capable of recording a digital video signal in the LPmode without degrading the tone quality of an audio signal.

Under this object, a digital signal recording apparatus which isarranged according to this invention comprises video input means forreceiving a digital video signal; audio input means for receiving nchannel digital audio signals (n: an integer which is at least 2); videocompressing means for compressing an amount of information of thedigital video signal; recording means for recording the digital videosignal and the digital audio signals on a recording medium; and modechangeover means for changing over the apparatus between a plurality ofmodes which includes a first mode in which the digital video signalsupplied from the video input means without passing through the videocompressing means and all of the n channel digital audio signalssupplied from the audio input means are recorded by the recording means,and a second mode in which the digital video signal having the amount ofinformation compressed by the video compressing means and only part ofthe n channel digital audio signals supplied from the audio input meansare recorded by the recording means.

It is a further object of the invention to provide an audio signalrecording apparatus which is of the kind having the amount ofinformation recordable per unit time variable and is arranged to becapable of recording a desired audio signal even when the amount ofinformation recordable per unit time is reduced.

Under that object, a digital signal recording apparatus arrangedaccording to this invention comprises input means for receiving nchannel digital audio signals (n: an integer which is at least 2);compressing means for compressing an amount of information of each ofthe n channel digital audio signals supplied from the input means; andrecording means for selectively recording on a recording medium eitherthe n channel digital audio signals having the amount of informationcompressed by the compressing means or n/m channel digital audio signals(m: an integer which is at least 2 and less than n) among the n channeldigital audio signals supplied from the input means without passingthrough the compressing means.

These and other objects and features of this invention will becomeapparent from the following detailed description of embodiments thereoftaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing in outline the arrangement of theconventional digital VTR. FIG. 2 is a block diagram showing the circuitarrangement of a digital VTR which is arranged as an embodiment of thisinvention. FIG. 3 is a block diagram showing the circuit arrangement ofthe essential parts of a digital VTR which is arranged as anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 shows in a block diagram the circuit arrangement of a digital VTRwhich is arranged as an embodiment of this invention. Referring to FIG.2, input terminals 51, 52 and 53 are arranged to receive the luminancesignal component Y and chrominance signal components PR and PB of avideo signal, respectively. Input terminals 60, 61, 62 and 63 arearranged to receive four channel audio signals of channels ch1, ch2, ch3and ch4, respectively. A/D converters 54, 55 and 56 are arranged todigitize the signal components Y, PR and PB supplied from the inputterminals 51, 52 and 53, respectively. A/D converters 66, 67, 68 and 69are arranged to digitize the analog audio signals supplied from theinput terminals 60 to 63, respectively. Compression circuits 57, 58 and59 are arranged to compress the amount of information of video dataoutput from the A/D converters 54, 55 and 56 to 1/2, respectively, bycarrying out a high efficiency encoding process such as predictivedifferential encoding. Compression circuits 72, 73, 74 and 75 arearranged to compress the amount of audio data output from the A/Dconverters 66, 67, 68 and 69 to 1/2, respectively, by carrying out acompounding differential encoding process or the like. Adders 78 and 79are arranged to multiplex on the time base the outputs of thecompression circuits 72 and 73 with those of the compression circuits 74and 75, respectively. Switches 82 and 83 are arranged to select theoutputs of the A/D converters 66 and 67 or the outputs of the adders 78and 79, respectively. Switches 86, 87, 88 and 89 are arranged to selectthe channels to be recorded. Switches 97, 98 and 99 are arranged toselect the outputs of the A/D converters 54, 55 and 56 or the outputs ofthe compression circuits 57, 58 and 59, respectively.

A control circuit 90 is arranged to control the switching actions of theswitches 82, 83 and 86 to 89. External switches 92 and 94 are providedon an operation panel for giving instructions for the switchingpositions of the switches 86 to 89. A changeover switch 93 is arrangedto switch the SP (standard-time) mode over to the LP (long-time) modeand vice versa. Memories 96V and 96A are similar to the memories 38V and38A shown in FIG. 1. Video data and audio data stored in the memories96V and 96A are arranged to be supplied to a video encoder 100 and anaudio encoder 101 to be subjected to recording processes, respectively.The processed video and audio data are time-base multiplexed with eachother by an adder 102. The output of the adder 102 is supplied via anamplifier 103 to a rotary head 104 to be recorded on a magnetic tape105.

The operation in the SP mode of the VTR of FIG. 2 is first described asfollows: in this instance, the SP/LP changeover switch 93 is operated tocause an SP/LP changeover signal to be output from the control circuit90. The SP/LP changeover signal shifts the connecting positions of theswitches 97, 98 and 99 to their contacts "a", respectively. Further, byusing the SP/LP changeover signal, the control circuit 90 connects theswitches 82 and 83 to their contacts "a" and brings the switches 86 to89 into their closed states.

Under this condition, the video signals supplied to the input terminals51, 52 and 53 are digitized, respectively, by the A/D converters 54, 55and 56. The digital video data thus obtained are supplied to the memory96V via the terminals "a" of the switches 97, 98 and 99, respectively.The audio signals supplied to the input terminals 60 to 63 aredigitized, respectively, by the A/D converters 66 to 69. The data outputfrom the A/D converters 66 and 67 are supplied to the memory 96A via thecontacts "a" of the switches 82 and 83 and the switches 86 and 87,respectively. The data output from the A/D converters 68 and 69 aresupplied to the memory 96A via the switches 88 and 89, respectively. Thevideo and audio data stored in the memories 96V and 96A are read out inthe same manner as in the case of the example of the conventional VTRdescribed in the foregoing. These data are then respectively subjectedto the recording signal processing actions of the encoders and 100 and101. The outputs of the encoders 100 and 101 are multiplexed with eachother at the adder 102. The output of the adder 102 is recorded on themagnetic tape 105 through the recording amplifier 103 and the rotaryhead 104.

Next, the operation in the LP mode of the VTR is described as follows:in the LP mode, the SP/LP changeover signal causes the switches 97, 98and 99 to be connected to their contacts "b". The video signals from theinput terminals 51, 52 and 53 are supplied via the A/D converters 54, 55and 56 to the compression circuits 57, 58 and 59 to have the amount ofinformation thereof compressed to 1/2, respectively. The compressedvideo data thus obtained are supplied to the memory 96V. Therefore, inthis case, the amount of information of the video data supplied to theadder 102 becomes 1/2 of the amount of information supplied in the SPmode. Then, assuming that the rotary head 104 is arranged to record onetrack per one rotation in the SP mode, the rotary head 104 makes tworotations to record one track in the LP mode. Further, it is assumedthat the traveling speed of the tape 105 in the LP mode is 1/2 of thespeed set for the SP mode.

In the LP mode, the audio data is recorded as follows: to ensure aboutthe same degree of tone quality in the LP mode as the quality attainablein the SP mode, this embodiment is arranged to record only two channelaudio signals among the four channel audio signals. In this instance,the external switch 92 is turned on to select a 2-channel audio mode. Inthe 2-channel audio mode, arbitrary two of the switches 86 to 89 areclosed while the rest are opened. If the switches 86 and 87 are arrangedto be closed in this instance, the control circuit 90 connects thecorresponding switches 82 and 83 to their contacts "a". As a result,arbitrary two channel audio signals among the four channel audio signalsof the channels ch1 to ch4 are supplied to the memory 96A. After that,the two channel audio signals are recorded on the magnetic tape 105 withthe same tone quality as in the SP mode.

In cases where a lower tone quality is allowable for the LP mode thanthe tone quality obtainable in the SP mode, all of the four channelaudio signals are recorded. In that instance, the external switch 94 isturned on to select a 4-channel audio mode. In the 4-channel audio mode,the control circuit 90 connects the switches 82 and 83 to their contacts"b" and closes the switches 88 and 89. As a result, the data output fromthe A/D converters 66 to 69 are compressed by the compression circuits72 to 75. The compression circuits 72 to 75 are arranged, for example,to compress a PCM code of 16 bits into a code of 8 bits. The adders 78and 79 add the output data of the compression circuits 74 and 75 tothose of the compression circuits 72 and 73, respectively. The data rateof the outputs of the adders 78 and 79 becomes the same as the rateobtained in the SP mode. The outputs of the adders 78 and 79 aresupplied to the memory 96A via the switches 82 and 83 and the switches86 and 87, respectively. As a result, the memory 96A stores all of thefour channel, audio signals, although they are in the compressed state.After that, these signals are subjected to the processing action forrecording in the same manner as in the SP mode before they are recordedon the magnetic tape 105 along with the video data.

In the case of the embodiment shown in FIG. 2, the number of channelsfor recording and the tone quality are arranged to be selectable by theoperator by selecting the 2-channel audio mode or the 4-channel audiomode. However, this arrangement may be changed to have one of the twoaudio modes automatically selected according to the incoming audiosignals. An example of such a modification is shown in FIG. 3.

FIG. 3 is a block diagram showing in outline the arrangement of theessential parts of a digital VTR which is another embodiment of theinvention. In FIG. 3, the same component elements as those of FIG. 2 areindicated by the same reference numerals. Referring to FIG. 3, theembodiment includes filters 110, 111, 112 and 113 which are arranged todivide the frequencies of each of the output data of the A/D converters66 to 69 into a low band L which is around 20 Hz, a medium band M whichis around 10 KHz and a high band H which is around 20 KHz. Determiningcircuits 116, 117, 118 and 119 are arranged to determine the tonequality on the basis of the band outputs L, M and H of each of thefilters 110, 111, 112 and 113. A control circuit 122 is arranged tocontrol the switches 82, 83 and 86 to 89 as stated in the foregoingaccording to the result of determination made by the determiningcircuits 116 to 119.

Each of the determining circuits 116 to 119 comprises, for example,integrating circuits which are arranged to integrate the band outputs L,M and H of each of the filters 110 to 113 and comparison circuits whichare arranged to compare the outputs of the integrating circuits withthreshold values set according to their dynamic ranges. Thesedetermining circuits are thus arranged to determine the audio signals asto whether they include all the components including the low, medium andhigh bands or only the low or medium band. The control circuit 122selects the 2-channel recording (2-channel audio mode) if the inputaudio signals have a high tone quality or the 4-channel recording(4-channel audio mode) if the input audio signals have a low tonequality.

As apparent from the foregoing description, the digital VTR described iscapable of carrying out recording in the LP mode without lowering thetone quality of the recording audio signals. Further, another advantageof the VTR lies in that the audio recording mode in which priority isgiven to the number of channels or the mode in which priority is givento tone quality is selectable as desired according to the purpose,nature, etc., of the audio signals to be recorded.

What is claimed is:
 1. A digital signal recording apparatus,comprising:a) compressing means for compressing a number of bits of eachsample of N channel digital audio signals N being an integer 2 or more;and b) recording means for recording a digital video signal and one of afirst digital audio signal which has N channels and is processed throughsaid compressing means and a second digital audio signal which has N/Mchannels and is obtained without passing through said compressing means,M being an integer 2 or more, an amount of information of the digitalvideo signal are determined irrespective of whether the first audiosignal or the second audio signal is recorded.
 2. An apparatus accordingto claim 1, wherein the amount of information per unit time of the firstdigital audio signal is equal to that of the second digital audiosignal.
 3. An apparatus according to claim 1, wherein said recordingmeans includes N/M time-base multiplexing circuits arranged to time-basemultiplex every M channel digital audio signals included in the firstdigital audio signal, and N/M switching circuits arranged to selectivelyoutput either the digital audio signals output from said N/M time-basemultiplexing circuits or the second digital audio signals.
 4. Anapparatus according to claim 1, wherein said recording means is arrangedto selectively record on the recording medium, in accordance with anoperation performed on a manual operation member, the first digitalaudio signal or the second digital audio signal.
 5. An apparatusaccording to claim 1, wherein said recording means includes determiningmeans for determining a tone quality of at least one of the N channelsof the first digital audio signal, and is arranged to selectively recordon the recording medium, according to an output of said determiningmeans, either the first digital audio signal or the second digital audiosignal.
 6. An apparatus according to claim 5, wherein said determiningmeans includes a separation circuit arranged to separate the digitalaudio signal into different frequency components.
 7. A digital signalrecording apparatus comprising:a) compressing means for compressing anumber of bits of each sample of a digital audio signal having aplurality of channels; b) recording means for recording a digital videosignal and a digital audio signal on a recording medium; and c) modechangeover means for changing over said apparatus between a plurality ofmodes, said plurality of modes including: a first mode in which a firstdigital video signal and a first digital audio which has a plurality ofchannels and is processed through said compressing means are recorded bysaid recording means; and a second mode in which a second digital videosignal and a second digital audio signal which has less number ofchannels, and is obtained without passing through said compressing meansare recorded by said recording means, wherein an amount of informationof the first digital video signal is substantially the same as thesecond digital video signal.
 8. An apparatus according to claim 7,wherein said plurality of modes further include a third mode in which athird digital audio signal which has the same number of channels as thefirst digital audio signal and is obtained without passing through saidcompressing means is recorded by said recording means.
 9. An apparatusaccording to claim 7, wherein the amount of information per unit time ofthe first digital audio signal to be recorded in said first mode isequal to that of the second digital audio signal to be recorded in saidsecond mode.
 10. An apparatus according to claim 7, wherein saidrecording means includes a plurality of multiplexing circuits arrangedto time-base multiplex every plural number of channels of the firstdigital audio signal, and a plurality of number of switching circuitsarranged to selectively output, in response to said mode changeovermeans, the digital audio signals output from said plurality of time-basemultiplexing circuits or the second digital audio signal.
 11. Anapparatus according to claim 7, wherein said mode changeover means isarranged to effect changeover between said first mode and said secondmode in response to an operation performed on a manual operation member.12. An apparatus according to claim 7, wherein said mode changeovermeans includes determining means for determining a tone quality of atleast one of the channels of the first digital audio signals, and isarranged to effect changeover between said first mode and said secondmode according to an output of said determining means.
 13. An apparatusaccording to claim 12, wherein said determining means includes aseparation circuit arranged to separate the digital audio signal intodifferent frequency components.